The present invention relates to a punch press, and in particular it relates to improvements in a fluid operated punch press.
Punch presses are used to form sheet metal. In one known type of punch press, a large flywheel is used to supply the energy needed to force a punch through a metal workpiece and into a die. The flywheel is connected with the punch through a crank mechanism which transmits the energy stored in the flywheel to the punch by converting the rotary motion of the flywheel into axial motion of the punch.
Another type of punch press, disclosed in U.S. Pat. No. 3,450,037, utilizes compressed air to power a piston in a cylinder. The piston is connected with the punch, and when air under pressure is introduced into the cylinder, the punch is driven downward through the workpiece. During its downward stroke, the piston obtains a high speed which is only partially dissipated by the impact of the punch with the workpiece. Various mechanisms have been designed to bring the piston to a halt at the bottom of its power stroke.
In a punch press mechanism which is disclosed in U.S. Pat. No. 3,545,368, a cylinder and a die are each mounted on a rigid plate. Return springs serve to return the piston to the top of its stroke. When air is introduced into the cylinder, the piston and guide rods move downward through a power stroke compressing the springs.
During operation of this type of press the piston is returned to the top of its stroke by the return springs with substantial velocity and kinetic energy. Prior art devices have utilized resilient bumpers at the top of the cylinder to absorb the energy of the fast moving piston. These resilient bumpers may deteriorate and permit the piston to impact the top of the cylinder with a substantial force. This is not only harmful to the press but may cause objectionable noise.